New Brown Dwarfs and an Updated Initial Mass Function in Taurus

Luhman, K. L.

doi:10.1086/425647

Cited by 227 publications

(388 citation statements)

References 74 publications

(251 reference statements)

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“…More quantitatively, we can calculate the number of brown dwarf to stars, defined been found in other 1-2 Myr old clusters (0.13 in IC 348, 0.18 in Taurus, 0.26 in Cha I, and 0.44 in NGC 1333, Luhman et al 2003b;Luhman 2004bLuhman , 2007Scholz et al 2012, respectively). However, this ratio is highly dependent on the accuracy of the spectral classification at the substellar limit.…”

Section: The Imfmentioning

confidence: 91%

Spectroscopy of new brown dwarf members ofρ Ophiuchi and an updated initial mass function

Oliveira¹,

Moraux²,

Bouvier³

et al. 2012

A&A

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Aims. To investigate the universality hypothesis of the initial mass function in the substellar regime, the population of the ρ Ophiuchi molecular cloud is analysed by including a new sample of low-mass spectroscopically confirmed members. To that end, we have conducted a large spectroscopic follow-up of young substellar candidates uncovered in our previous photometric survey. Methods. The spectral types and extinction were derived for a newly found population of substellar objects, and its masses estimated by comparison to evolutionary models. A thoroughly literature search was conducted to provide an up-to-date census of the cluster, which was then used to derive the luminosity and mass functions, as well as the ratio of brown dwarfs to stars in the cluster. These results were then compared to other young clusters. Results. It is shown that the study of the substellar population of the ρ Ophiuchi molecular cloud is hampered only by the high extinction in the cluster ruling out an apparent paucity of brown dwarfs. The discovery of 16 new members of ρ Ophiuchi, 13 of them in the substellar regime, reveals the low-mass end of its population and shows the success of our photometric candidate selection with the WIRCam survey. The study of the brown dwarf population of the cluster reveals a high disk fraction of 76 +5 −8 %. Conclusions. Taking the characteristic peak mass of the derived mass function and the ratio of brown dwarfs to stars into account, we conclude that the mass function of ρ Ophiuchi is similar to other nearby young clusters.

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Section: The Imfmentioning

confidence: 91%

Spectroscopy of new brown dwarf members ofρ Ophiuchi and an updated initial mass function

Oliveira¹,

Moraux²,

Bouvier³

et al. 2012

A&A

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“…Photoionizing radiation from massive OB stars might contribute by removing much of the envelope and disk of a low-mass protostar (Hester et al 1996;Kroupa & Bouvier 2003a;Whitworth & Zinnecker 2004). Alternatively, turbulent compression and fragmentation of gas in a molecular cloud produces collapsing cores over a wide range of masses (Padoan & Nordlund 2002, 2004Hennebelle & Chabrier 2008;Elmegreen 2011). VLMSs and BDs then arise from the smallest cores.…”

Section: Theory: Star-like Bd Formationmentioning

confidence: 99%

“…Taurus exhibits a paucity of high-mass young stars (Kenyon et al 2008) and was originally proposed to be deficient in low-mass stars (Briceño et al 2002) as well. Many brown dwarfs have however since been discovered (Luhman 2004;Guieu et al 2006). Kroupa et al (2003) and Thies & Kroupa (2008) show that there is no need to invoke a non-canonical IMF in Taurus.…”

Section: The Stellar and Substellar Population Inmentioning

confidence: 99%

Using binary statistics in Taurus-Auriga to distinguish between brown dwarf formation processes

Marks¹,

Martín

Béjar

et al. 2017

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Context. Whether brown dwarfs (BDs) form just as stars directly from the gravitational collapse of a molecular cloud core ("star-like") or whether BDs and some very low-mass stars (VLMSs) constitute a separate population which form alongside stars comparable to the population of planets, e.g. through circumstellar disk ("peripheral") fragmentation, is one of the key questions of the star-formation problem. Aims. For young stars in Taurus-Auriga the binary fraction has been shown to be large with little dependence on primary mass above ≈ 0.2M⊙, while for BDs it is < 10%. Here we investigate a case in which BDs in Taurus formed dominantly, but not exclusively, through peripheral fragmentation, which naturally results in low binary fractions. The decline of the binary frequency in the transition region between star-like formation and peripheral formation is modelled. Methods. A dynamical population synthesis model is employed in which stellar binary formation is universal with a large binary fraction close to unity. Peripheral objects form separately in circumstellar disks with a distinctive initial mass function (IMF), own orbital parameter distributions for binaries and a low binary fraction according to observations and expectations from smoothed particle hydrodynamics (SPH) and grid-based computations. A small amount of dynamical processing of the stellar component is accounted for as appropriate for the low-density Taurus-Auriga embedded clusters. Results. The binary fraction declines strongly in the transition region between star-like and peripheral formation, exhibiting characteristic features. The location of these features and the steepness of this trend depend on the masslimits for star-like and peripheral formation. Such a trend might be unique to low density regions like Taurus which host dynamically largely unprocessed binary populations in which the binary fraction is large for stars down to M-dwarfs and low for BDs. Conclusions. The existence of a strong decline in the binary fraction -primary mass diagram will become verifiable in future surveys on BD and VLMS binarity in the Taurus-Auriga star forming region. It is a test of the (non-)continuity of star formation along the mass-scale, the separateness of the stellar and BD populations and the dominant formation channel for BDs and BD binaries in regions of low stellar density hosting dynamically unprocessed populations.

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“…The original measurements were in the R C and I C filters for those targets reported in Kenyon & Hartmann (1995), whilst all other compiled literature studies transformed the measured photometric value into the Cousins system (Guieu et al 2007(Guieu et al , 2006Luhman 2000Luhman , 2004Luhman et al 2003a;Briceño et al 1999Briceño et al , 2002Martín et al 2001). For targets with more than one photometric measurement, the median value was adopted.…”

Section: Construction Of Spectral Energy Distributionsmentioning

confidence: 99%

The Taurus Boundary of Stellar/Substellar (TBOSS) Survey

Bulger

Patience

Ward-Duong

et al. 2014

A&A

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With the PACS instrument on Herschel, 134 low mass members of the Taurus star-forming region spanning the M4-L0 spectral type range and covering the transition from low mass stars to brown dwarfs were observed. Combining the new Herschel results with other Herschel programs, a total of 150 of the 154 M4-L0 Taurus members have observations, and we have added an additional 3 targets from Spitzer to form the 153-object TBOSS (Taurus Boundary of Stellar/Substellar) sample, a 99% complete study. Among the 150 targets, 70 µm flux densities were measured for 7 of the 7 Class I objects, 48 of the 67 Class II objects, and 3 of the 76 Class III objects. For the detected Class II objects, the median 70 µm flux density level declines with spectral type; however, the distribution of excess relative to central object flux density does not change across the stellar/substellar boundary in the M4-L0 range. Connecting the 70 µm TBOSS values with the results from K0-M3 Class II members results in the first comprehensive census of far-IR emission across the full mass spectrum of the stellar and substellar population of a star-forming region, and the median flux density declines with spectral type in a trend analogous to the flux density decline expected for the central objects. Spectral energy distributions (SEDs) were constructed for all TBOSS targets covering the optical to far-IR range and extending to the submm/mm for a subset of sources with longer wavelength data. Based on an initial exploration of the impact of different physical parameters on the Herschel flux densities, geometrical factors such as inclination and structural parameters such as scale height and flaring have the largest influence on the flux densities in the PACS bands. From the 24 µm to 70 µm spectral index of the SEDs, 5 new candidate transition disks were identified. Considering the previously known and new candidate transition disks, the spectral indices over longer wavelengths (≥70 µm) are not distinct from those of the full Class II population, suggesting that the outer regions of the transition disks are similar to Class II disks. The steep 24 µm to 70 µm slope for a subset of 8 TBOSS targets may be an indication of truncated disks in these systems, however additional measurements are required to establish the outer radii of these disks conclusively. From existing high angular resolution companion search observations, two examples of mixed pair systems that include secondaries with disks were measured in the Herschel data. Finally, comparing the TBOSS results with a Herschel study of Ophiuchus brown dwarfs reveals a lower fraction of disks around the Taurus substellar population with flux densities comparable to the Ophiuchus disks.

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New Brown Dwarfs and an Updated Initial Mass Function in Taurus

Cited by 227 publications

References 74 publications

Spectroscopy of new brown dwarf members ofρ Ophiuchi and an updated initial mass function

Spectroscopy of new brown dwarf members ofρ Ophiuchi and an updated initial mass function

Using binary statistics in Taurus-Auriga to distinguish between brown dwarf formation processes

The Taurus Boundary of Stellar/Substellar (TBOSS) Survey

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